Wire-format constants for the LookupKey ZMQ admin channel.
This is the single source of truth shared by LookupKeyClient and LookupKeyServer on the scheduler<->worker rank-0 admin channel.
Wire format (REQ/REP over IPC):
Request: [msg_type: bytes] [payload_frames...]
msg_type == LOOKUP_MSG:
frame 1: token_len (u32 big-endian, 4 bytes)
frame 2..n: msgpack-encoded list[str] of block-hash hex digests
Response: [hit_count: u32 big-endian, 4 bytes]
msg_type == RESET_MSG:
(no payload frames)
Response: [RESP_OK] or [RESP_ERR]
The first frame of every request is a named bytes tag (not a numeric sentinel that aliases the data field) so the protocol stays self-describing and extensible: adding new admin commands requires only a new tag and a new dispatch branch.
Mirrors the named-tag convention used by the NIXL connector (see vllm/distributed/kv_transfer/kv_connector/v1/nixl/metadata.py).